I have a fair understanding about the formation of the Mormon Church. Especially what happened in Carthage Illinois. And I do know about the things he did that lead up to his murder.
Surely you do not suggest that Joseph Smith had any chance of being President of the U.S. That is just plain silly.
No, what I am saying is that the Later Day Saints have been a political and religious group from their founding. Their goal has always been to obtain political power in order to change the US Constitution to reflect the beliefs of Mormonism. Joseph Smith did not agree with the idea of constitutional representative government. He believed in theocracy where all authority comes from the Mormon leader who is a god and must be obeyed without question. His ‘church’ remains a totalitarian organization to this day.
Therefore, when Romney demands a loyalty oath from members of the Republican Party, he is being true to his Mormon beliefs about authority.